Net zero ready homes use unique geothermal solution
After completing a historic geothermal project in 2009 for the first "net-zero" residential development in New York state — and probably the nation — Lloyd Hamilton was ready for a new challenge. That's exactly what he got when Anthony Aebi, president of Greenhill Contracting Inc., Rhinebeck, New York, asked him to devise a geothermal solution to heat and cool nine "net-zero-ready" homes in nearby Mountain Vista, New York.
"When I worked with Anthony in 2009, I was thrilled to be his HVAC and building energy consultant," says Hamilton, a certified geothermal designer and president of Verdae, LLC, also located in Rhinebeck. "We were making history. The original new-zero development was called Green Acres. It consisted of 25 high-end homes in New Paltz, New York, each incorporating insulated concrete form (ICF) construction, solar panels and a WaterFurnace Envision geothermal system. The selling point for these homes was tremendous comfort and indoor quality, plus an annual heating and cooling energy cost that came to zero. In fact, most of the homes made some money by selling electricity back to the utility.
"Now after the recession, Anthony called me about a cluster development called The Preserve. He wanted these nine homes to also be zero-energy concept, but cost about 20 percent less. That meant finding a way to reduce costs overall, including geothermal installation costs."
For affordability, Aebi located The Preserve development in the Mountain Vista area, where land costs less. The remote location also meant municipal water was not available. So Abei asked Hamilton if each well for each home could do double duty: both to supply domestic water and to serve as a closed-loop heat-exchange well.
From the builder's viewpoint, Anthony Abei notes that, "The issue with water-source geothermal is that if anything ever goes wrong with a well, you have to drill a new one. The other issue is that you have to drill a well in the first place. The idea of using only one well was intended to address both these issues.
The request put Hamilton in a different situation from the 2009 project. "Before, all the homes in Green Acres were on the municipal water supply. That meant we had to bore holes averaging 400 feet deep in dense rock for a dedicated closed-loop, vertical heat exchange well. Drilling through 400 to 500 feet of rock just for the water-source loop is expensive.
"Anthony figured using one well for both domestic water and a heat exchange well would cut down on drilling costs," says Hamilton. "Plus, it would cut the maintenance costs associated with open-loop wells, which typically involve a source well and an injection well that gets bogged down with mineral deposits from return water disposal.
"I did some research and found the only issue with using one well was getting enough room to make the closed loop fit. So we instructed the driller to bore an eight-inch well, rather than a six-inch well."
Hamilton determined the well depth using GeoLink Design Studio, WaterFurnace's geothermal design and energy analysis software. He input the load information and the model — in this case, the WaterFurnace 7 Series variable-capacity model NV036 with three-ton capacity. There was no need to plug a water heater into the program, because the electricity generated by each home's solar panels would power a stand-alone electric water heater.
Hamilton selected a vertical loop type with one u-bend with an average loop depth from the well to the house of eight feet. After inputting the dense soil type and the minimum and maximum loop temperatures, the program determined the depth of the bore.
"We came up with an average 400-foot well depth with 100 feet of pipe to the house," says Abei. "Doubling those numbers comes to between 875 to 1200 feet of polyethylene pipe in each loop."
Compared to other closed loop water-source installations, that length is short. Hamilton could get away with the short length because homes in The Preserve have an air-tight building envelope and high R-value ICF construction, which substantially reduces the heating and cooling load.
"I actually see my job as much as a commissioning agent for whole-home efficiency," says Hamilton. "As defined by ASHRAE, that role involves figuring out the owner’s interests and helping them achieve their goals. I understand how the house functions. The shell needs to work properly. The indoor environment needs to be easy to control. The indoor air quality, comfort and durability of the building need to be solid. All of these factors reduce the load and, consequently, the first cost of the geothermal system."
As a result of the load reduction, Hamilton notes that he could select the smaller, three-ton WaterFurnace 7 Series model. "New York has incentives for builders who build ENERGY STAR® homes. Talking with the ENERGY STAR program managers at the NY level, they agreed that these homes could meet ENERGY STARY Home designation by running the 7 Series at a speed that meets the Manual J load calculation. Typically, that turned out to be speed six.
"The WaterFurnace 7 Series is designed to fit in so many situations," he continues. "It has 14 stages of heating and 12 stages of cooling. So for example, it can run at 60 percent of capacity or less and meet the cooling load. The neat thing is, the unit can run at any speed down to one, so you can have it running at very low speed at very high efficiency."
In this case, the speed reduction achieved an efficiency that is "far beyond the ENERGY STAR requirement," says Pasquale Strocchia, who works as a LEED for Homes Green Rater (USGBC) and HERS Rater (RESNET) for Integral Building and Design in New Paltz.
"The Preserve homes have several energy certifications," Strocchia notes. "First, they have a HERS index of less than 5. Anything less than 15 is considered net-zero capable. The HERS index scale goes from 0 to 100. A zero is, of course, a net-zero energy home.
"All of Anthony’s homes are less than seven. The minimum HERS index for an ENERGY STAR home is about 75. So all his homes easily meet the ENERGY STAR requirement.
"In my experience, WaterFurnace has always been right in front in terms of the prevalence of units. The feedback I receive from homeowners with existing systems is generally very positive."
Chrissy and Al Roth, who moved into The Preserve on Oct. 21, 2013, have positive feelings. "We knew Anthony had built the Green Acres community in our area," says Chrissy. "But it was out of our means at the time. We lived in a condominium with a boiler and an air-conditioning system that needed a few window air conditioners, too. It was highly inefficient. Making the move to an environmentally designed home was what we wanted to do.
"Boy, did it pay off. Even in the worst of the 2014 winter, our January energy bill was just $100. And that was keeping our 2,350-square-foot home at 72 degrees for 24 hours a day. When my brother and sister visited us, they said it was remarkable to go into every room and have the exact same temperature — downstairs, upstairs, our bedroom, our bathroom, up in the attic — everything was the same. The WaterFurnace system along with the ICF walls and eighteen- to twenty-inch insulation in the ceiling makes a huge difference."
Lloyd Hamilton is pleased to be part of another successful Abei net-zero project. "For The Preserve development, the loop is the unique thing that I did. We were able to piggyback the closed loop inside the water well. That saved on drilling costs and site disruption."
"With the loop being immersed directly in well water, we get high thermal efficiency that takes full advantage of the 7 Series variable-speed capabilities. That is important, because we’re in a heating dominated climate. And it's an environmentally friendly solution, too, because we can just use plain water in the loop instead of glycol, because the well water doesn't freeze. It's a win-win-win that worked really well for everybody."
Read more about geothermal heating and cooling.